This invention relates to an air induction system for supplying air to an internal combustion engine through an air intake tube. More particularly, this invention relates to an air induction system that includes a thermal pump having a variable volume gas chamber operably coupled to the air intake tube and responsive to temperature for drawing hydrocarbon vapors from the air intake tube to prevent escape of hydrocarbon vapors when the engine is not operating.
In an automotive vehicle, air is supplied to an internal combustion engine through an air intake tube, referred to as a zip tube, connecting an air cleaner canister and an air intake manifold of the internal combustion engine. When the engine is turned off, residual fuel may produce hydrocarbon vapors in the intake manifold. There is concern that the hydrocarbon vapors may diffuse through the air intake tube and become emitted into the atmosphere. It has been proposed to include a material, such as porous carbon or zeolite, within the air induction system to absorb vapors diffusing from the intake manifold. The absorbed vapors are then desorbed into the air stream when the engine is again operated, whereupon the vapors are consumed in the engine. While various arrangements have been considered, it is desired not to restrict the air flow path through the air intake tube so as to provide the needed air supply during engine operation. As a result, while the hydrocarbon absorbing material may be located to absorb a significant portion of the hydrocarbon vapors, it is nevertheless possible for some vapors to flow through the tube and be emitted into the atmosphere:
In addition to the concern over residual fuel vapors in the intake manifold when the hot engine is turned off, there is also concern about emission of hydrocarbon vapors that may occur when the engine sits idle for an extended period of time and is exposed to variations in ambient temperature. For this purpose, it is common practice to measure hydrocarbon emissions that occur during a diurnal test that cycles the ambient temperature between 65xc2x0 F. and 105xc2x0 F. Under these conditions, vapors that were absorbed by the vapor absorbing material may be desorbed into the air flow path and migrate into the atmosphere.
Therefore, a need exists for an air induction system for an internal combustion engine that is effective to draw off air containing hydrocarbon vapors that is attempting to migrate through the air intake tube when the engine is turned off to prevent the vapors from being emitted into the atmosphere and to return the vapors to the air intake manifold when the engine is restarted for combustion in the engine. In addition to capturing residual fuel vapors from the air intake manifold immediately after the hot engine is turned off, it is also desired that the air induction system draw off air from the intake manifold during periods of fluctuating ambient temperature to capture any hydrocarbon vapors therein and so prevent their emission into the atmosphere.
In accordance with this invention, an improved air induction system is provided for an internal combustion engine that includes an air intake tube. The air induction system includes a bladder that defines a variable volume gas chamber. The gas chamber is coupled to the air intake tube for drawing gas into the gas chamber. The volume of the gas chamber varies in response to temperature between a deflated condition at a first, relatively low temperature and an inflated condition at a second, higher temperature. Thus, as the temperature increases, the bladder inflates to draw off gas from the air intake tube that may contain hydrocarbon vapors and thereby prevent the vapors from escaping through the air intake tube into the atmosphere.
In an aspect of this invention, the gas chamber is also variable in response to the operation of the internal combustion engine, regardless of temperature. When the engine is operating, suction produced by the engine to draw air through the air intake tube and the intake manifold also draws air from the gas chamber to deflate the bladder. As a result, when the engine is turned off, the bladder is in a deflated condition despite the elevated temperature due to engine operation. Thereafter, because of the elevated temperature, the gas chamber inflates to draw air from the air intake tube. In this manner, hydrocarbon vapors migrating from the intake manifold through the air intake tube are drawn into the gas chamber and prevented from emission.
In another aspect of this invention, the air induction system includes a hydrocarbon vapor absorbing material, and the gas chamber is operatively coupled to the hydrocarbon vapor absorbing material for expelling gas thereto. Thus, during temperature cycling, the gas chamber inflates as the temperature increases to draw gases from the air induction tube and prevent vapor escape therethrough. Thereafter, as the temperature decreases, the gas chamber deflates to expel gas to the hydrocarbon vapor absorbing material so that the hydrocarbon vapors may be suitably absorbed.
In a preferred embodiment of this invention, the air induction system includes a thermal pump that comprises the bladder and means for inflating and deflating the bladder. This includes at least one element having a variable length responsive to temperature and attached to the bladder for flexing the bladder between the deflated condition and the inflated condition.
In still a further aspect of the preferred embodiment of this invention, the bladder includes at least one panel that flexes to vary the bladder between the deflated condition and the inflated condition. An arm is attached to the panel and includes an outboard portion. A first bimetallic spring is pivotably connected to the outboard portion at a first point and extends in a first direction. A second bimetallic spring is pivotably connected to the outboard portion at a second port outboard to the first point and extends in a second direction generally opposed to the first direction. The first and second bimetallic springs have lengths that vary in response to temperature, preferably so that the springs expand at higher temperatures. As the temperature increases, the springs cooperate to swing the arm between a first position corresponding to the bladder in the deflated condition and a second position corresponding to the bladder in the inflated condition, thereby inflating the bladder and drawing vapor-containing air into the gas chamber. Thereafter, as the temperature decreases, the bimetallic springs cooperate to swing the arm to deflate the bladder and expel the vapor-containing air, for example, for combustion in the engine or absorption by a storage media.